But I get it enough to realise, if that can be done why hasn't it?

If all was as simple as that way of putting out things... gosh... maybe I am getting old and slow... Anyway, everyone is doing what they can/able. Just because an idea looks good, it sometimes doesn't mean it should be implemented. There is more that needs to be done around it, like context, strategy, long term planning, consequences prediction/studies... I know this is all an experiment, but it's a very complex and large scale one with an unprecedented number of reasons it will forever be in the Crypto History. So, not as easy as it might look at first sight anymore. Anyway... I should shut... otherwise you going to fall asleep.

Wouldn't it be a positive for Hive to recover the funds in those zombie accounts?

My idea is to recover the account name, not the funds. Although in my detailed explanation I did not consider the liquid ones (that would effectively be taken over). The staked ones though would be lost. And the vision behind it is to de-incentivise attacks to "steal" funds from zombie accounts. I don't wanna promote robbery, the idea is to balance the ideological view of the effort perceived when trying to exploit blockchains, improving the relation between the two ends (good and bad).

Apart from inflated user numbers, why would so many idle accounts be needed?

You need to research a bit more. There are multiple reasons why accounts are created and sometimes not used. Most of them are actually with good intentions and/or reasons. But the main purpose of my idea was actually to protect/change the view of the desire to exploit. Some people just wanna do bad things because of hate or jealous. The beauty of open tech is that you can't think what is "right" you have to think as "everyone" might think. Otherwise, you are doomed to fail to face what you should be prepared to deal with when you were not.

I suggest you keep reading more. You seem to want to know more, and I can only tell you it will give you more clarity about the subjects you seek the answer to.